This invention relates generally to locomotive fuel usage, and more specifically, to a method and apparatus for evaluating locomotive fuel efficiency and usage as determined by the locomotive operator""s handling of the train during a given train run.
Large self-propelled traction vehicles, such as locomotives, commonly use a diesel engine to drive an electrical transmission system comprising a generator for supplying electric current to a plurality of direct current traction motors, whose rotors are driving coupled, through speed-reducing gearing, to the respective axle-wheel sets of the vehicle. The generator typically comprises a 3-phase traction alternator whose rotor is mechanically coupled to the output shaft of the engine, typically a 16-cylinder turbo-charged diesel engine. When excitation current is supplied to field windings of the rotating rotor, alternating voltages are generated in the 3-phase stator windings. The output voltage is rectified and applied to the armature windings of the traction motors. The diesel engine may also be driving coupled to an auxiliary alternator for supplying alternating current at a constant frequency to the various auxiliary systems on the locomotive or on the cars pulled by the locomotive.
During the xe2x80x9cmotoringxe2x80x9d or propulsion mode of operation, a locomotive diesel engine delivers constant power from the traction alternator to the traction motors, depending on the throttle setting and ambient conditions, regardless of the locomotive speed. For maximum performance, the electrical power output of the traction alternator must be suitably controlled so that the locomotive utilizes full engine power. For proper train handling, intermediate power output levels are provided to permit graduation from minimum to full output. But the traction alternator load on the engine must not exceed the level of power the engine is designed to develop for a given speed. Overloads can cause premature wear, engine stalling or xe2x80x9cbogging,xe2x80x9d or other undesirable effects. Historically, locomotive control systems have been designed so that the operator can select the desired level of traction power, in discrete steps between zero and maximum, so that the traction and auxiliary alternator, driven by the engine, can supply the power demanded by the traction load and the auxiliary loads, respectively.
In the prior art locomotives, when the throttle is advanced from one position to the next (commonly referred to as notches) the diesel engine speed and/or the load (or excitation) applied to the traction motors are simultaneously increased to the speed and horsepower point established for the new notch position. Some notch position changes may involve only a speed change, others only a horsepower change and still others a change in both the engine speed and delivered horsepower. The engine acceleration to the new speed point is controlled by the electronic fuel injection controller that adjusts the quantity of pressurized diesel fuel (i.e., fuel oil) injected into each of the engine cylinders so that the actual speed (in rpm) of the crankshaft corresponds to the desired speed. If the new notch position also commands a new horsepower value, the locomotive control system applies more excitation to the main alternator, which in turn supplies more current to the traction motors, increasing the motor horsepower.
The engine electronic fuel injection controller controls the engine speed in response to speed changes requested by the locomotive control system by way of a notch position change made by the locomotive operator. Generally, the fuel injection controller does not receive any signals from the throttle when it is changed from one notch position to another and therefore does not know when a notch change has occurred. Instead, the speed governor knows only the speed demand as requested by the locomotive control system. In fact, there may be multiple notch settings that vary the horsepower delivered by the traction motors without changing the engine speed.
For each of its eight different notch settings, the engine is capable of developing a corresponding constant amount of horsepower (assuming maximum output torque). When the throttle notch 8 is selected, maximum speed (e.g., 1,050 rpm) and maximum rated gross horsepower (e.g., 4,500) are realized. The engine power at each notch equals the power demanded by the electric propulsion system, which is supplied by the engine-driven traction alternator, plus the power consumed by the electrically driven auxiliary equipment.
The locomotive fuel system includes a tank, a low pressure subsystem, and a high pressure subsystem. A typical diesel locomotive tank has a capacity of 5,000 gallons. A low pressure pump provides approximately seven gallons per minute (at 40 pounds per square inch (psi)) from the tank to a fuel header which supplies fuel to the high pressure pumps. Each cylinder has its own high pressure pump. In turn, the high pressure pump injects the fuel into a fuel injector at each diesel engine cylinder at a pressure of between 18,000 and 20,000 psi. At idle, approximately only 10% of the fuel drawn for the fuel tank by the low pressure pump is used for combustion. At notch 8, the percentage rises to approximately 60% to 70%. A pressure regulator interposed between the low pressure pump and high pressure pump bleeds off the unburned excess fuel not used for engine combustion and returns it to the fuel tank via a drain line. Also, the high pressure delivered by the high pressure pumps, causes some fuel to leak from the fuel injectors. This unused fuel is collected from the injectors and also drained back to the fuel tank. Typically, a 16-cylinder diesel engine has one fuel injector drain for each 8-cylinder block.
An electronic fuel injection controller provides a pulse input to high pressure pump solenoids that drive high pressure pumps and thereby control the injection of fuel into each cylinder. The leading edge of the pulse sets the start of fuel injection, and the pulse length determines the duration of fuel injection into the cylinder. The pulse duration determines the fuel mass that is injected into each cylinder, as measured in mm3/injection. Look-up tables provide the required start of injection timing as a function of engine speed and fuel value, which is a measure of the volume of fuel being injected into each cylinder.
The efficient functioning of diesel locomotive engines, especially as it relates to fuel usage, is an important factor in the operational costs of the railroad. Periodically, diesel locomotive engines are tested for output to determine whether a repair or overhaul is necessary. Various testing methods are used, with one common test employing a dynamo meter for measuring the mechanical output power of the engine. Another method utilized in the prior art simply considers the total miles run or diesel engine operational horsepower-hours. It is recognized, however, that these methods do not allow for precise analysis of the engine condition due to variations between engines, especially engine combustion conditions.
The most efficient method of determining engine condition is to measure the actual amount of fuel consumed by the engine per unit of work. In accord with the dual pump system discussed above, the measurement of fuel consumption requires four flow meters, with one flow meter on each of the three return lines and a fourth flow meter on the supply line. The four flow meter readings must be summed to calculate the amount of fuel used by the diesel engine. This is not accomplished without difficulty, due to inherent inaccuracies in the system and measuring devices and further the expense associated with installing such a system. But, given the high fuel costs, generally the highest cost element associated with operation of a railroad, it is especially important to ensure the locomotives are in excellent operating condition and further that the locomotive operators employ efficient operational techniques to contain the fuel costs.
In addition to budget matters, in day-to-day train operation, it is especially important to monitor the quantity of fuel remaining in the tanks or conversely the quantity of fuel used since the tank was filled to avoid running the fuel tank dry. Freight trains typically include up to six locomotives, coupled together at the front of the train or employed as pusher or helper locomotives distributed among the freight cars. Each locomotive is self-contained and includes its own fuel tank. In most train systems of the prior art, there has been no reliable or convenient technique for measuring the amount of fuel in each tank. Even experienced train operators have been surprised to find their fuel tank suddenly empty midway between fueling terminals. Obviously, such a situation creates considerable expense for the railroad and inconvenience to the freight owner.
Fuel gauges are used on locomotives, but most are not accessible to the train crew while the train is moving. Instead, some locomotives are provided with a sight glass, which can measure the top 1000 gallons of fuel in the tank. Other locomotives are equipped with float gages that can be read by an observer on the ground when the train is stopped. These float gages are known to be inaccurate and cannot be read from walkway along the locomotive cab or from inside the cab. Hence, these gages cannot be used while the train is moving.
There are also several types of electronic fuel gages used on locomotives. One such gage employs a pressure sensor at the bottom of the fuel tank. The sensor produces a voltage proportional to the amount of fuel remaining in the tank and transmits the voltage value to the cab, where it is converted to a display indicative of the approximate quantity of fuel remaining in the tank.
Another exemplary fuel gage employs a bubble-type fuel measuring system. The system operates by measuring the pressure exerted by the fuel in a bubble tube positioned near the bottom of the fuel tank. In one embodiment, the system employs several bubbling tubes located at predetermined locations in the tank and positioned a fixed height from the tank bottom. A predetermined volume of air flow is forced through the tubes. Pressure transducers periodically measure the air pressure supplied to the bubbling tubes respectively. A microprocessor converts the pressure data to determine the average normalized pressure that the fuel exerts at the bottom of the tank and then from that determines the level of fuel remaining in the tank. Since the volume of air bubbled into the tank is constant, the pressure required to bubble a given volume will be greater when the tank is fuller. As fuel is consumed and the fuel level drops, the pressure required to bubble the same volume of air into the tank is reduced. The accuracy of this bubble-type fuel measuring system depends in large measure on the health of the pneumatic components of the system. If, for example, there are any air leaks in the system, the pressure sensed at the bubble tube will be influenced by the atmospheric back-pressure thereby rendering the measured fuel readings inaccurate.
While some of the electronic and pneumatic systems currently available enable the to train crew to monitor fuel levels while the train is moving, most do not provide for the monitoring of fuel levels in a locomotive where no crew members are present, for instance in a consist of several locomotives where only the lead locomotive has an operator. If the locomotive operator must determine the fuel available in the locomotive consist, the train must be stopped and the gauge in each locomotive checked individually.
To evaluate the various methods of train operation, for example, the time at which the locomotive is switched from one notch position to another, and the use of stretch braking (the simultaneous application of motive power and brakes, as a technique to control the train at the expense of fuel consumption), it would be advantageous to know the maximum amount of fuel that should be used by a locomotive during a run. To date, measurement complexity has allowed the determination of this value only in a laboratory. According to the present invention, it is possible to determine, with fairly significant accuracy, the amount of fuel that an ideal locomotive is expected to use during a given run, based on an algorithm derived from laboratory analysis and the amount of time the locomotive spends at each engine speed (or notch position) during the run. An ideal locomotive will use a derivable quantity of fuel in each notch position and this quantity can be calculated. It is noted that the ideal fuel quantity is not dependent on the topography encountered during the run or speed limitations, etc., because it is based solely on the notch position (or engine speed) and the horsepower delivered. Although the calculation is derived for a so-called xe2x80x9cidealxe2x80x9d locomotive, in practice it has been determined that the ideal values are within a few percentage points of the actual values. The difference between the values is influenced by, for example, the efficiency of the fuel system, fuel injector and pump wear and ambient conditions. In accordance with the teachings of the present invention, the ideal fuel usage can be determined and utilized to evaluate the locomotive operator""s ability to operate the train in a fuel efficient manner. Also, if the fuel quantity at the beginning of the run is known, the calculated quantity used can be subtracted from the initial value to derive the amount of fuel left in the tanks.
The present invention provides accurate calculation of ideal fuel usage by an onboard microprocessor, based on inputs that identify specific operational modes of the locomotive. The microprocessor calculates the ideal fuel usage based on the operating time in each mode and the ideal fuel usage factors associated with each mode. Determination of these fuel usage factors must be accomplished through laboratory measurements for locomotives of a given type or class. Tests have indicated that the ideal fuel usage calculated in accordance with the teachings of this invention offers an accuracy that rivals or even exceeds fuel usage measurements (or the fuel quantity remaining in the tanks) as determined by prior art mechanical, pneumatic, or electronic techniques. Since many of today""s operational locomotives include a microprocessor, implementation of the present invention requires only the inclusion of the algorithm of the present invention into the microprocessor memory for execution.
Although the system according to the present invention does not provide any indication of the absolute operating efficiency of the locomotive, it does, however, provide a tool to evaluate the performance of a locomotive operator and the methods of train handling employees.